thx dsull for the explanation. that makes sense. I manage to create the drosophila genome using the following command (I copied it from your github repository.
kb ref --workflow=standard -i index.idx -g t2g.txt -f1 Drosophila_melanogaster.BDGP6.46.cdna.fa \
--include-attribute gene_biotype:protein_coding \
--include-attribute gene_biotype:lncRNA \
--include-attribute gene_biotype:lincRNA \
--include-attribute gene_biotype:antisense \
--include-attribute gene_biotype:IG_LV_gene \
--include-attribute gene_biotype:IG_V_gene \
--include-attribute gene_biotype:IG_V_pseudogene \
--include-attribute gene_biotype:IG_D_gene \
--include-attribute gene_biotype:IG_J_gene \
--include-attribute gene_biotype:IG_J_pseudogene \
--include-attribute gene_biotype:IG_C_gene \
--include-attribute gene_biotype:IG_C_pseudogene \
--include-attribute gene_biotype:TR_V_gene \
--include-attribute gene_biotype:TR_V_pseudogene \
--include-attribute gene_biotype:TR_D_gene \
--include-attribute gene_biotype:TR_J_gene \
--include-attribute gene_biotype:TR_J_pseudogene \
--include-attribute gene_biotype:TR_C_gene \
Drosophila_melanogaster.BDGP6.46.dna.toplevel.fa Drosophila_melanogaster.BDGP6.46.112.gtf